Slidable window for x-ray microanalyzers selectively permeable to hard or soft x-rays



I May 9, 1967 Filed Aug. 24, 1964 J. GUERNET ETAL SLIDABLE WINDOW FOR PERMEABLE TO HARD OR SOFT X-RAYS Fig.1

X-RAY MICROANALYZERS SELECTIVELY 2 Sheets-Sheet 1 May 9, 1967 J. GUERNETETAL 3,319,064

SLIDABLE WINDOW FOR X-RAY MICROANALYZERS SELECTIVELY v PERMEABLE TO .HARD OR SOFT X-RAYS Filed Aug. 24, 1964 2 Sheets-Sheet 2 mmmmm v I M 5 9 M) United States Patent 3,319,064 SLIDABLE WINDOW FOR X-RAY MICROANA- LYZERS SELECTIVELY PERMEABLE T0 HARD 0R SOFT X-RAYS Jacques Guernet and Jean-Michel Rouberol, Paris, France, assignors to Compagnie dApplications Mecaniques a lElectronique, au Cinema et a IAtomistique Filed Aug. 24, 1964, Ser. No. 391,630 Claims priority, application France, Aug. 27, 1963,

45,748, Patent 1,375,173 2 Claims. (Cl. 250-49.5)

. emitted by the various elements present in the sample at the point of impact of the beam.

The X-rays pass from the first to the second enclosure through an opening which may be closed, for example in the case when the two enclosures are not at the same pressure, by a membrane which is transparent, at least to a certain degree, to X-rays.

The first enclosure has to be highly evacuated, say at about 10" mm. Hg, mainly to allow the electron optics system to be operated at a high voltage.

It is also useful to establish a vacuum in the second enclosure in order to avoid the X-rays being absorbed by the air. However, in this case, the vacuum need not be so high, as for a pressure of 0.1 mm. Hg, the absorption of X-rays is practically negligible.

The X-rays window has to absorb as little X-rays as possible and has to withstand a pressure of about one atmosphere, so that the vacuum may be removed from one of the enclosures. These two requirements are in fact somewhat contradictory.

Since no window is known which is sufficiently transparent to X-rays, while being capable of withstanding a pressure difference of one atmosphere, the best solution so far used was to place a removable and sufficiently strong window between the two enclosures. This window was normally collapsed or retracted and the same high vacuum was established in both enclosures. However, the window was replaced in position when the vacuum in one of the enclosures had to be removed. This arrangement has the drawback of requiring a powerful pumping system, since, in this case, the two enclosures have to have a high vacuum, which is very difiicult to obtain in the second enclosure since:

(a) The volume of the enclosure containing the spectrometer is greater;

(b) The spectrometer includes some moving parts which have to be lubricated with grease, with a vapour pressure higher than mm. Hg;

(c) The spectrometer parts release a large amount of (d) A type of counter which is currently used as receiver in X-ray spectrometers is the gas circulation counter, whose entrance window, generally of very thin plastic film, continuously releases a certain amount of gas.

It is an object of the invention to provide an improved seal arrangement between the two enclosures of an X-r-ay microanalyzer. An arrangement according to the invention consists of a set of membranes which allow X-rays to pass from one enclosure to the other with practically negligible absorption and yet make it possible to estab- Patented May 9, 1967 lish a large pressure difference between the two en closures, in one direction or the other.

According to the invention, the partition wall, commor to the two enclosures, is provided with one or more openings which can be closed at will,

(a) Either by extremely'thin windows causing practicall'y no absorption of even very soft X-rays, but capable of withstanding only a very low pressure difference and thus fragile;

(b) Or by windows much stronger than the former and capable of withstanding a pressure difference of one atmosphere, i.e. permitting letting air into one enclosure or the other, but suificiently transparent to hard X-rays to be used for the analysis of such rays.

When the latter window or windows are in working position the fragile window or windows are put in such a position that both their sides-are at the same pressure, so that this pressure may vary, for example when air is let in, without fracturing these fragile windows.

The invention will be better understood from the following description with reference to the appended drawings, wherein:

FIG. 1 is the diagram showing the principle of an X-ray microanalyzer; and

FIG. 2 and FIG. 3 show two positions of the arrangement according to the invention.

FIG. 1 shows an X-ray microanalyzer of known type.

This microanalyzer consists of a vacuum-tight enclosure 1 containing a cathode 21 and an electron optics system, including a cylindrical control electrode 22, an accelerator anode 23 and electromagnetic focusing lenses 24 and 25, which directs an electron beam onto a sample 3 to be analyzed. At the point of impact the beam diameter is about In.

The X-ray spectrometer is placed in a second enclosure 4, generally of a much greater volume. It comprises a monochromator crystal 5, which receives the X-rays emitted by the sample, and a radiation counter 6. The

X-rays pass from enclosure 1 to enclosure 4, through an opening, which can be closed by a window 7.

During an analysis, a high vacuum has to be made in enclosure 1, whereas it may be suflicient to lower the pressure to 0.1 mm. Hg in enclosure 4, to avoid the X-rays being absorbed by the air.

An arrangement according to the invention is shown in FIGS. 2 and 3. By way of example enclosure 4 includes two spectrometers which respectively analyze the X-rays emitted in directions X X and X X the first spectrometer being intended for the analysis of hard X-rays and the second of soft X-rays.

This arrangement includes, between enclosures 1 and 4, a support 7 carrying a set of windows 11, 12 and 13. This support is slidably mounted at 8 and can take up two different positions along the partition wall between enclosures 1 and 4, shown respectively in FIGS. 2 and 3. On FIG. 2, windows 11 and 12 are in register with two openings 21 and 22 in the partition wall common to enclosures 1 and 4. In FIG. 3, these openings are in register with windows 12 and 13. In both positions, the unused windows, i.e., windows 13 or 11, have their both sides in enclosure 1, at the same pressure.

Windows 11, 12 and 13 are provided with toroidal seals to ensure that enclosure 1 is vacuum tight.

Windows 11 and 12 withstand a pressure difference of one atmosphere. They are made of beryllium.

Window 13 is a fragile collodion window.

In FIG. 2, window 13 is not used. This position is used when air has to be let into enclosure 4 (in this case large pressure difference exists on the two sides of the wall, and the windows have to be strong) or when analyzing hard X-rays (in this case the fragile window is unnecessary).

The position shown in FIG. 3 corresponds to the case hen soft X-rays are being analyzed. In this case, a high acuum has to be established in enclosure 4 in order to nsure minimum absorption of soft X-rays. Window 3 is used. It does not have to resist strong stresses, since 1e pressure is substantially the same in enclosure 1 and nclosure 4.

Thus a system of this kind has the advantage of making 1e equipment vacuum-tight, whatever the pressure diference between the two enclosures, the fragile window eing used only for low pressure difference. In this case, n account of its small thickness, it absorbs a minimum f soft X-rays.

The invention is of course not restricted to the above vrrangement, which is shown and described only by way If a non limitative example.

What is claimed is:

1. An X-ray microanalyzer for analyzing samples, com- I rising: a first enclosure; a sample to be analyzed and in electron optics system for providing an electron beam .triking said sample, said sample and said electron optics :ystem being located in said first enclosure; a second on :losure, an X-ray analysis system located in said second :nclosure for analyzing the X-rays emitted by said sample; 1 partition wall between said enclosures, said wall havng at least one opening; a first movable window perneable to soft X-rays; a second movable window perneable to hard X-rays and capable of withstanding pressure difference on its faces; and means external of said enclosures for selectively bringing in register with said opening either one of said windows.

2. An X-ray microanalyzer for analyzing samples, comprising: a first enclosure; a sample to be analyzed and an electron optics system for providing an electron beam striking said sample, said sample and said electron optics system being located in said first enclosure; a second enclosure, an X-ray analysis system located in said second enclosure for analyzing the X-rays emitted by said sample; a partition wall between said enclosures, said wall having at least one opening; a support slidably mounted along said wall in one of said enclosures, said support comprising at least one window permeable to soft X-rays and at least one window permeable to hard X-rays and capable of withstanding pressure diflFerence on its faces; and means external of said enclosures for displacing said support for selectively bringing in register with said opening either one of said windows.

References Cited by the Examiner UNITED STATES PATENTS 9/1937 Horsley et a1. 250-86 OTHER REFERENCES RALPH G. NILSON, Primary Examiner.

A. B. CROFT, Assistant Examiner. 

1. AN X-RAY MICROANALYZER FOR ANALYZING SAMPLES, COMPRISING: A FIRST ENCLOSURE; A SAMPLE TO BE ANALYZED AND AN ELECTRON OPTICS SYSTEM FOR PROVIDING AN ELECTRON BEAM STRIKING SAID SAMPLE, SAID SAMPLE AND SAID ELECTRON OPTICS SYSTEM BEING LOCATED IN SAID FIRST ENCLOSURE; A SECOND ENCLOSURE, AN X-RAY ANALYSIS SYSTEM LOCATED IN SAID SECOND ENCLOSURE FOR ANALYZING THE X-RAYS EMITTED BY SAID SAMPLE; A PARTITION WALL BETWEEN SAID ENCLOSURES, SAID WALL HAVING AT LEAST ONE OPENING; A FIRST MOVABLE WINDOW PERMEABLE TO SOFT X-RAYS; A SECOND MOVABLE WINDOW PERMEABLE TO HARD X-RAYS AND CAPABLE OF WITHSTANDING PRESSURE DIFFERENCE ON ITS FACES; AND MEANS EXTERNAL OF SAID ENCLOSURES FOR SELECTIVELY BRINGING IN REGISTER WITH SAID OPENING EITHER ONE OF SAID WINDOWS. 